The present invention relates to a sputtering target assembly having a precipitation hardened backing plate diffusion bonded to a sputtering target.
There has been growing interest in sputtering target assemblies with increasingly thin sputtering targets to reduce costs and, in some cases, accommodate the sputtering target assembly in certain sputtering chambers. In such applications, sputtering target assemblies of less than about one inch total thickness may be required. However, with such sputtering target assemblies, the strength of the backing plate may be exceeded under the conditions encountered in the sputtering chamber, which may include high water pressure on one side for cooling and high vacuum on the other side during the sputtering process. Thermal cycling and pressure resulting from circulating coolant exerted upon the backside of the target assembly with simultaneous vacuum conditions on the front face of the target can result in elastic and plastic deformation of the target backing plate assembly.
Although sputtering target assemblies may be made by solder bonding backing plates of various materials to a target, solder bonding has the disadvantage of not being able to withstand high power sputtering applications. Thus, diffusion bonded sputtering target assemblies are preferred.
The present invention provides a method of making a sputtering target assembly with a high strength backing plate diffusion bonded to a sputtering target that can withstand the stresses and strains typically encountered in sputtering chambers.
According to the invention there is provided a method of making a heat treated sputtering target assembly that comprises providing a sputtering target and a heat treatable, precipitation hardenable backing plate diffusion bonded to the sputtering target wherein the diffusion bonded sputtering target assembly is heat treated to precipitation harden the backing plate without delaminating or degrading the diffusion bond between target and backing plate. The method comprises precipitation hardening the backing plate by heat treatment that includes quenching the diffusion bonded sputtering target assembly by the process includes heating, working, and quenching and the quenching is performed after diffusion bonding by immersing the sputtering target assembly in a quenchant to immerse the backing plate without submerging the sputtering target. The sputtering target assembly may be subjected to a plurality of precipitation hardening treatments that include heating and partial-immersion quenching, as described, to provide a desired temper in the backing plate. In a preferred embodiment, the backing plate comprises a heat treatable aluminum alloy of the 2000, 6000 or 7000 series and the sputtering target comprises aluminum, titanium, or nickel, titanium-tungsten, tungsten, cobalt and tantalum and alloys thereof. The sputtering target assembly of the invention comprises a precipitation hardened backing plate diffusion bonded to a sputtering target.